Technical Field
This disclosure relates to the rendering of images on displays, or on display areas having a resolution and/or an aspect ratio differing from those of the original image.
Description of the Related Art
Given the numerous image formats (still or video), with a variety of resolutions and aspect ratios, it often happens that a display is not adapted to the original image, for example when viewing a 4/3 video on a 16/9 display, or vice versa. The formats for still pictures are even more varied, whereby more difficulties are encountered.
In some applications, it is desired to display a mosaic of images, such as thumbnails of a photo album, or sub-pictures often called Picture-In-Picture (PIP) from multiple sources. Thumbnails or sub-pictures may have an aspect ratio close to 1, while the sources may have an aspect ratio of 16/9 or 4/3, or other ratios, such as for photos.
FIG. 1 illustrates two conventional rendering techniques that may be used to display a 16/9 image (left) in a square thumbnail (right), for example.
In the upper thumbnail, the original image's aspect ratio is preserved. The scaling of the original image is calculated to match the largest dimension of the image to a side of the square. The modified image is centered vertically in the square, and black bands are displayed in the areas of the square corresponding to no image. Part of the thumbnail is not used to display the image.
In the lower thumbnail, the image is transformed to fill the square. For this purpose, the vertical and horizontal dimensions of the original image undergo different scaling factors. The entire surface of the thumbnail is used to display the image, but the image has a vertical stretch distortion.
Moreover, visual quality deterioration may often be perceived in the thus processed images, even when using sophisticated scaling algorithms.